In earlier work, we identified a novel intracellular antiproliferative protein which we call prohibitin, and showed that prohibitin could block DNA synthesis in normal human fibroblasts and HeLa cells in vitro. In our most recent work, we have shown that prohibitin is highly conserved in evolution, expressed as a function of the stage of the cell cycle, and may play a role in processes as diverse fruit fly development and human breast cancer.